A building board, for example a floorboard, provided with a projecting metal strip formed with a locking element for mechanical joining is described in WO 94/26999. The content of that document shall be considered to be part of the present description, and provides a more detailed description of how such building boards can be designed and joined together. The background, features and advantages of the invention will be described specifically for this known type of floorboard, but it should be emphasised that the invention is useful for making building board types other than floorboards, such as wall panels and roof slabs. All references to the term "floor-board" should therefore be considered to apply to building boards in general.
WO 94/26999 thus discloses a system for mechanical joining of floorboards. A first mechanical connection provides mutual vertical locking of the joint edges and may be in the form of a tongue-and-groove joint along the joint. A second municipal connection provides mutual horizontal locking of the boards in a direction at right angles to the joint edges of the boards.
In order to illustrate the situation upon which the present invention is based, reference is now made to FIG. 1, which shows in section a joint between two identical mechanically joined floorboards 2. The method according to the invention is useful for making such floorboards. The design and the function of the floor-boards 2 substantially correspond to what is known from WO 94/26999. However, there are certain differences compared to the prior art with respect to the geometrical shapes of a gripping stud and a locking element.
Each board 2 has a top side 4 and underside 6 and, for illustration purposes, can be assumed to be made of a board body S of laminated fibreboard, plastic composite, wood or the like. The thickness of the body S can, for example, be 7 mm. To enable a mechanical connection, opposite joint edges 8 of the boards 2 are formed with an integrated metal strip 10 mounted at the factory, as well as a locking groove 16. The strip 10 is preferably made of sheet aluminium and extends horizontally from the underside 6 of the board 2 in the direction of the second floorboard and runs continuously throughout the entire length of the joint. However, the strip 10 can be divided into smaller parts, which cover the main portion of the length of the joint.
In order to achieve the required joint tolerances as well as simple laying, the strip 10 is integrally formed with the board, i.e. it is mounted at the factory and should specifically not be mounted in connection with laying. As a non-restrictive example, the strip 10 may have a width of about 30 mm and a thickness of about 0.6 mm. Metal sheet materials other than aluminium could also be used.
Along its one side edge, the strip 10 is formed with a locking element 12, bent from the sheet material, which exhibits an active locking surface 14 having a height of e.g. 1.0 mm. In the joined state, the locking element 12 is received in a locking groove 16, formed in the underside 6 of the second board and extending parallel to and spaced from the joint edge 8. The locking element 12 and the locking groove 16 together form the above-mentioned second mechanical connection, locking the boards 2 to each other in the direction designated D2. More specifically, the locking surface 14 of the locking element 12 serves as a stop with respect to the surface 18 of the locking groove 16 closest to the joint edges 8.
When the boards 2 are joined together according to FIG. 1, they can occupy a relative position in the direction D2 where a small play .DELTA., as small as 0.01 mm, exists between the locking surface 14 and the locking groove 16. This play makes it possible to displace the boards 2 in the direction of the joint without the use of tools. This displaceability facilities the laying and enables joining together the short sides by snap action. Reference is made to WO 94/26999 for a more detailed description of the function and advantages of this construction.
The strip 10 is mounted in a tolerance-equalising groove in the underside 6 of the board 2. In this embodiment, the width of the equalising groove is approximately equal to half the width of the strip 10, i.e. about 15 mm. The functioning of and different ways of forming the equalising groove are described in detail in WO 94/26999 and, consequently, need not be repeated here.
The strip 10 is mechanically fitted to the body S in the following manner. A groove 20 is provided in the underside 6 of the body S at a distance from a recess 22 adjacent to the joint edge 8. The groove 20 may be formed either as a continuous groove extending throughout the entire length of the body S, or as a number of separate grooves. Together with the recess 22, this groove 20 defines a dove-tail gripping stud 24 of the body S. In its fastened state in FIG. 1, the strip 10 exhibits a number of punched and bent tongues 26 as well as one or more lips 28, which are bent round opposite sides of the gripping stud 24. The term "gripping element" will be used in the following as a general term for tongues, lips and corresponding components of the strip which are formed from the sheet material and bent round the gripping stud 24 of the body S.